dipper@utastro.UUCP (Debbie Byrd) (11/07/84)
An astronomer predicted Mercury would transit the sun on this date in 1631. More on why this prediction was important -- after this. November 7 Kepler's Transit of Mercury On today's date in the year 1631 a French astronomer -- Pierre Gassendi -- made the first recorded observation of a transit of Mercury across the face of the sun. A transit occurs when -- from our point of view on Earth -- an inner planet appears to move in front of the sun. This transit of Mercury in 1631 had been predicted four years before -- by an astronomer working on a revolutionary problem. Johannes Kepler was born less than thirty years after publication of the theory that the Earth and other planets move around the sun. Kepler was a mathematician -- who proved it was wrong to think that the planets orbit the sun in perfect circles. His calculations showed that the orbits of the planets are really ellipses -- more like circles that've been squashed. In 1627 Kepler published tables listing the movements of the planets. He included a prediction that Mercury would transit the sun in 1631. Previous transits of Mercury had not been seen because the planet is invisible to the naked eye in the course of a transit -- lost in the solar glare. By 1631 telescopes had come into use -- and Pierre Gassendi used a telescope and solar filter to prove that Kepler was correct -- Mercury did transit the sun just when he said it would. Kepler didn't live long enough to see his prediction confirmed -- he died the year before. But the laws he postulated for the orbits of planets helped usher in modern astronomy. Script by Diana Hadley. (c) Copyright 1983, 1984 McDonald Observatory, University of Texas at Austin